Learning objective: Designing K-12 schools: HVAC systems
In K-12 schools, technological advancements, code requirements, and other demands placed on engineers are consistently increasing, while limitations like budget restraints remain a challenge. HVAC systems, air quality, and acoustics are discussed here.
- David Ellis, PE, CEM, LEED AP Senior Vice President of Engineering Allen & Shariff Engineering LLC Columbia, Md.
- Nestor Ortiz Senior Construction Engineer, Project Officer Parsons Brinckerhoff Long Island City, N.Y.
- John C. Palasz, PE, HFDP Mechanical Engineer Primera Engineers Ltd. Chicago
CSE: What unique HVAC requirements do K-12 school structures have that you wouldn't encounter on other structures?
Ellis: Acoustical standards stand out as the differentiator, as system-based noise has detrimental impacts on learning, much more so than the same levels have on office production or other similar activities. Maintenance staff may not have the training to adequately support complex systems, and as such require system operation and maintenance to be as straightforward as possible; with complex systems, such as related to renewable energy systems, it may be outsourced for ongoing support.
CSE: What changes in fans, variable frequency drives, and other related equipment have you experienced?
Ellis: The biggest change in the design approach has been the introduction of de-coupling of ventilation from conditioning by the use of DOAS, and the application of VRF systems. DOAS allows for substantial energy savings in the avoidance of conditioning unnecessary ventilation air, and VRF allows for low-energy transport of heat during periods of concurrent heating and cooling. Of course, improvements in design and cost of variable frequency drives (VFDs) allows for more opportunities for implementing the energy-saving advantages associated with variable flow, both air and water, and development of inexpensive pressure independent constant air regulators allows for the mixing of constant and variable flow ventilation on the same variable air volume (VAV) DOAS, which allows for ventilation savings with highly variable occupancy classrooms with fixed makeup spaces, such as labs.
Palasz: Over the past few years, I have experienced a change in the trend of using a roof-mounted return fan in an insulated housing (similar to a rooftop unit) to wrapping a mixed flow fan. This results in a lighter and more efficient design, which helps to decrease initial costs by reducing the structural reinforcement requirements. It also helps to improve the return on investment with a very efficient fan (up to 85% efficient).In regard to VFDs, they have become less expensive and more widely used to provide system flexibility and soft-start capability in addition to diagnostic alarms.
CSE: Do you find it more challenging to retrofit HVAC systems on older buildings than installing on new?
Palasz: Yes, I find it more challenging to retrofit HVAC systems because the older buildings often have space limitations, structural limitations, and additional expenses due to building materials requiring abatement. This often requires a great deal of time and effort to survey the existing system as well as a great deal of documentation.Additionally, system deficiencies are often discovered during the site survey that can easily lead to an increase in scope. A diligent project manager can help define and track scope expectations clearly.